Alkylated aromatic amines, e.g., diarylamines, such as alkylated diphenylamine, are well known in the art to be effective stabilizers/antioxidants in a wide variety of organic materials, for example, polymeric substances such as natural or synthetic rubber, polyolefins, polystyrenes, condensation polymers, other elastomers and thermoplastics plastics, lubricating oils including e.g., mineral oil derived lubricants and synthetic lubricants, etc. In many these applications, light colored products which are liquid at room temperature are desirable.
A variety of catalysts have been used in the alkylation of aromatic compounds including protic acids, metal based Lewis acids such as aluminum trichloride, and clays. U.S. Pat. No. 3,496,230 discloses the preparation of a mixture of 80% dinonydiphenylamine and 15% nonyldiphenylamine in the presence of Friedel-Crafts catalysts such as AlCl3 and ZnCl2, but mixtures contaminated by traces of chlorine, metal compounds and undesirable by-products, e.g. N-alkylated diphenylamines and diphenylamines alkylated in the 2- and 2′-positions, are obtained, which mixtures are black in color and very viscous.
U.S. Pat. No. 2,943,112 discloses a two-step process whereby alkylation of diphenylamine in the presence of acid catalysts or clay catalysts with relatively unreactive olefins is followed by alkylation with more reactive olefins to scavenge the unreacted diphenylamine. Clay catalysts are reported to provide less color. U.S. Pat. No. 6,204,412 discloses a method of alkylating diphenylamine to obtain a light colored, liquid product, which also comprises a two-step method wherein, in the second step, a second olefin is added to the reaction mixture containing diphenylamine and diisobutylene (and/or an alpha-olefin of the disclosed formula) to scavenge or reduce the amount of unreacted diphenylamine in the product.
Often, mono-alkylation, di-alkylation and poly-alkylation are possible and control over the amount and position of alkylation, e.g., ortho-, para- etc., is required. U.S. Pat. No. 4,824,601 discloses the use of acidic clay catalysts for the alkylation of diphenylamine to produce a light colored, liquid product by reacting certain molar ratios of reactants within specific temperature ranges for a time sufficient to ensure the alkylated product contains less than 25% dialkylated diphenylamine. The limit on the amount of dialkylated diphenylamine is disclosed as necessary to avoid the formation of crystallized, solid products.
U.S. Pat. Nos. 5,672,752 and 5,750,787 disclose processes for alkylating diphenylamine with linear alpha olefins and diisobutylene in the presence of a clay catalyst, which selectively result in a higher proportion of monoalkylated diphenylamine and a lower proportion of unsubstituted diphenylamine and/or disubstituted or polysubstituted diphenylamines.
U.S. Pat. No. 6,315,925 discloses alkylating diphenylamine with an excess of nonene or a mixture of isomeric nonenes in the presence of from 2.0 to 25.0% by weight, based on diphenylamine, of an acidic clay in the absence of a free protonic acid, resulting in a mixture containing at least 68.0% dinonyldiphenylamine, from 20.0 to 30.0% nonyldiphenylamine, not more than 3.5% trinonyldiphenylamine; and not more than 1.0% diphenylamine.
Greater efficiency in the use of starting materials and generation of less waste for disposal is needed; for example, U.S. Pat. No. 8,828,916 discloses a process for preparing nonylated diphenylamines which improves nonenes usage by recycling and reusing stripped unreacted nonenes from an earlier process.
In the catalyzed processes above, the catalyst will become inactivated over time and will be discarded as contaminated waste. This is true for batch processes and continuous processes. A method for regeneration of spent catalyst would allow for the continued use of the catalyst which could reduce costs and waste.
Acidic clays, similar to those useful in alkylation of aromatic compounds, have also been used in industrial processes for removing colored impurities from mineral oils, as catalysts in cracking of hydrocarbons, and other operations. Methods for regenerating clays used in these heavy industry applications are known.
U.S. Pat. No. 2,368,507 discloses a method of regenerating catalysts, such as silica, alumina and acid treated bentonitic clays, useful in cracking, reforming, dehydrogenation or aromatization reactions of hydrocarbon oils, by treating the catalyst with air or hot inert gasses containing regulated quantities of air or oxygen at temperatures high enough to cause combustion of the carbonaceous materials deposited on the catalysts during use.
U.S. Pat. No. 2,102,341 discloses of method of regenerating materials used for decolorizing mineral oils, such as clays, by forming a slurry containing the spent clay in a non-acidic stable solvent in the presence of a volatile basic reacting substance, e.g., ammonia or volatile alkyl amines, which basic reacting substance is absorbed by the clay and thus displacing the absorbed matter on the surface of the spent clay, followed by separating the solvent and displaced matter from the clay and basic reacting substance, and then removing the basic reactive substance from the clay.
U.S. Pat. No. 3,148,158 discloses a process for activating a raw, unused bentonite clay by removing impurities such as certain magnesium, calcium and iron compounds as well as other impurities, the process comprising treating the raw clay with a hydrolyzable inorganic or organic halide, e.g., thionyl chloride, in the presence of a small amount of water and an inert organic diluent, such as an ether, ketone, alcohol, alkane, aromatic hydrocarbon or other organic solvent, at a temperature ranging from ambient to 130° C.
U.S. Pat. No. 5,942,457 discloses a process for regenerating spent clay comprising (1) an extraction stage wherein an organic solvent or mixture of organic solvents are thoroughly mixed with the spent clay thus separating the entrained oil from the spent clay, (2) a reactivation stage wherein the oil-free spent clay is treated with acid, and (3) a thermal polishing step wherein the acid-treated, solvent extracted spent clay is heated at a temperature from 500° F. to 1400° F.
Many of the processes used in regenerating spent clay catalysts for removing colored impurities or in cracking of hydrocarbons etc., employ harsh conditions that may harm a catalyst used in alkylation, especially selective alkylation, of aromatic systems. A process is still needed for regenerating a clay catalyst used in the alkylation of aromatic compounds, e.g., aromatic amines, that is robust enough to remove the material deposited on the clay, e.g., oligomers, amine residues, reactant and product degradation products, etc., but which process does not harm the features of the catalysts that provide the desired reactivity and selectivity during the alkylation reaction.